1. Field of the invention
The present invention concerns a method of protecting against erosion and/or corrosion steam pipes of the high-pressure stage of a power and/or steam generation plant saturated steam turbine, at its low-pressure stage and at heaters of the heat exchanger installation of the power and/or steam generation plant, in which method the major part of the water contained in the wet steam outlets and offtakes of the high-pressure stage is separated out by centrifugal means, a first fraction of the steam partly dried by this means is superheated and/or final dried and then fed into the low pressure stage of the turbine and a complementary fraction of the partly dried steam is fed to the heaters. It also encompasses a device for implementing this method.
As is known, the steam from the offtakes or the outlet of the high-pressure stage of a saturated steam turbine is wet (water content approximately 10 to 20%). Because it flows at relatively high speed in the steam pipes, either to the low-pressure stage of the turbine or to the steam heaters of the heat exchanger installation of the power and/or steam generation plant, the water particles in motion cause relative rapid erosion and/or corrosion of the pipes.
It has already been proposed to reduce the water content of this steam to a sufficiently low value for it to produce no significant erosion and/or corrosion of the pipes. Use may be made for this purpose of high-speed centrifugal separators with coaxial tubular members supplying at the downstream end a coaxial flow of steam with reduced water content and a peripheral flow of water or of steam with a very much increased water content, of the kind described in particular in the documents EP-A-0002235, EP-A-0005493 and FR-A-2558741.
In this way the moisture content of the steam entering the downstream pipework can be reduced to less than 1%. Downstream of the low-pressure stage the steam is superheated and/or dried more thoroughly at the entry to the low-pressure stage of the steam turbine by means of superheaters comprising tubular heat exchangers with bundles of tubes through which the water vapor at higher temperature and at higher pressure passes and/or separators comprising bundles of parallel corrugated plates, the separator-superheaters being either vertical, of the kind described in the document EP-A-0010261, or horizontal, of the kind described in the document EP-A-0005225, for example.
FIG. 1 of the appended drawings is a schematic representation of a protection device of this kind.
The high-pressure portion 1 of the steam expansion turbine is on the same shaft lA as its low-pressure portions 34, 36, 38. The high-pressure portion comprises two series of wet steam outlets 2, 4 and 3, 5 adapted to be connected to the low-pressure portions by main pipes 20 and 21. Offtakes 6 and 7 are provided to feed respective heaters 22A and 23A of the heat exchanger installation of the power and/or steam generation plant, for example to heat the water supplied to the power and/or steam generation plant. The offtake pipes incorporate respective high-speed centrifugal separators 8, 10, 12 and 9, 11, 13.
Downstream of the high-speed centrifugal separators the pipes 14, 16 and 15, 17 discharge into the main pipes 20 and 21 to the low-pressure stage. The pipes 18 and 19 feed the steam to the heaters 22A and 23A previously mentioned.
The main pipes 20 and 21 feed the three low-pressure portions of the turbine. They are divided between pipes 22, 24, 26 and 23, 25, 27 incorporating separator-superheaters 28, 30, 32 and 29, 31, 33. The various streams of superheated and/or dried steam then discharge into the low-pressure portions 34, 36, 38.
This device makes it possible to prevent most erosion and/or corrosion of the feed pipes of the low-pressure expansion portions and heaters but requires the installation of a high-speed separator on each steam pipe. The necessary plant is therefore somewhat complex and costly.
An object of the invention is to provide a method and a device for protecting against erosion and/or corrosion steam outlet and offtake pipes from the high-pressure stage of the turbine and the pipes connecting to the low-pressure stage portions and to the heaters of the heat exchanger installation of the power and/or steam generation plant necessitating simpler and less costly plant for equally effective drying of the steam drawn off from the high-pressure stage.